The present invention relates to fluid filtering devices, more particularly, devices constructed using generally corrugated filter media in combination with flat media, hereafter, referred to as a xe2x80x98Honeycomb designedxe2x80x99 filtering element.
There exists an ongoing effort in the filtration industry to maximize filter life while simultaneously trying to reduce filter size, weight, and costs. These efforts are accomplished in part by maximizing the amount of media surface area which reduces pressure drop across the filter and prolongs its useful life. It is also desirable for the housing structure supporting the filter to be of a simplified design or even eliminated entirely. All of these factors, including the methods used for manufacturing the filter element, must be considered for maintaining low production costs.
Pleated paper filters with rigid housings have long been the industry standard for most filtering applications. These filters, however, generally require relatively expensive hardware such as centertubes and endcaps and have relatively low filter densities and load capacities.
Attempts have been made to increase the filter density and load capacity of filter elements. This has included the development of orthogonal flow filters, more commonly referred to as xe2x80x9cHoneycombxe2x80x9d filters.
FIGS. 1-3 depict a honeycomb filter and segments thereof which can be made from prior art methods. FIG. 1 illustrates a cylindrical filtering element 10. It is noted that fluid intake in this device is shown by arrows 16 and filtered fluids exit from the bottom end as shown by arrows 18. The filter element 10 typically includes an impervious barrier element 24 which is cylindrical in shape so as to be sized to receive the body of element 10 within. The purpose of barrier 24 is primarily to prevent entry of uncleaned fluid via the sidewalls of the element, thereby directing it in the flow shown by arrows 16.
FIG. 2 shows a fragmentary view of a portion of the top end of filtering element 10. Fluid 16 enters the filter through openings such as 38 and enter flutes which run essentially the length of element 10 but are plugged on the opposite end. Plugs 39 prevent entry of fluid 16.
As can be seen in FIG. 3, filtering occurs within element 10 due to alternating ends of adjacent flutes being sealed to prevent fluid transfer thereby forcing all fluid to pass through the media in order to exit the element. One possible flow pattern is shown wherein fluid 16 enters open flute 50 on the inlet of filter 10, is filtered across corrugated media layer 20 and exits via opening 32 on the outlet end of the filter. Alternatively, fluid 16 may be filtered sideways across the flat media layer 26 and exit via opening 34 at the outlet end of the filter. As fluids pass through a media wall, filtering occurs and particulate matter becomes lodged within the media itself. Because this loading will increase the face velocity at that point, particulate matter will tend to be collected at other points along the walls thereby evenly distributing the particulate matter throughout the filter until it is fully loaded.
This basic design for honeycomb filters is also well documented in the prior art. One such reference is U.S. Pat. No. 2,322,548 issued to Sigmund wherein an impervious board matrix separates a flat filtering sheet which is rolled into a cylindrical shape. Filtering occurs when the fluid entering the intake side must cross through the inner walls at a right angle to exit by the outlet side.
U.S. Pat. No. 2,210,397 issued to Dreiss uses a similar filtering scheme by carefully aligning two sheets of substantially flat filter paper with a specially designed top and bottom plates to direct airflow. U.S. Pat. No. 3,020,977 issued to Huppke et. al. introduces the additional feature of corrugated material between flat sheets, although the corrugated material performs no filtering function, but merely acts as a spacer. Likewise, U.S. Pat. No. 2,397,759 issued to Sigmund employs a corrugated member as a spacer.
None of the aforementioned references are able to achieve the high filtering density desired because of the use of construction materials which are merely structural, rather than material suited for performing both structural and performing a filtering function.
U.S. Pat. No. 4,410,427 issued to Wydeven was able to achieve the high filtering density desired in an orthogonal flow filter because of the use of materials which performed both a structural and a filtering function. Since Wydeven, numerous patents have been issued acknowledging the benefits of orthogonal flow filtering occurring from the use of honeycomb designed filters which include increased filter performance, reduced weight and overall outer dimension, as well as lower manufacturing costs.
Honeycomb filters provide benefits over other filter designs in certain applications. These benefits include: greater life expectancy, at equal efficiency; fixed geometryxe2x80x94no pleat bunching; more media per unit volume of filter; lower materials cost, for many applications; simple construction; and product differentiation.
Presently, honeycomb structures are being used throughout industry; offering advantages in many xe2x80x9cnon-filteringxe2x80x9d applications. Some of the areas where product advantages are currently being obtained as a result of the honeycomb design are: 1) Automotive Catalytic Converters; 2) Structural Components; 3) Packaging and Container Materials; 4) Heat Exchangers; 5) Shock Absorbing Materials; and, 6) Aerospace Structural Components.
Prior Art Method of Producing Honeycomb designed Filter Elements
Basically, round honeycomb filters FIG. 1 and panel honeycomb filters FIG. 12 are produced by corrugating filter media. The honeycomb filter comprises a corrugated filter media sandwiched between flat sheets of filter media on either side.
As described earlier and depicted in FIG. 1, round honeycomb filter elements comprise one flat sheet and one sheet of corrugated media layer positioned on top of the flat sheet, adhesively connected thereto and which forms a sheet of filter media which is subsequently rolled to form the filter element. For panel honeycomb filter elements, alternating layers of corrugated filter media and flat sheets are utilized, stacked on top of one another.
As defined here, xe2x80x9cprimary flutexe2x80x9d is the interior space between the corrugated media and first contact with the flat-sheet media. Prior art shows that the primary flutes are formed and sealed during the corrugating process.
As defined here, xe2x80x9csecondary flutexe2x80x9d is the interior space between the corrugated media and contact with flat-sheet media on the opposing side of the corrugated media. Prior art shows that the secondary flutes are formed and sealed during assembly of the filter element.
Use of the terms xe2x80x9cprimaryxe2x80x9d and xe2x80x9csecondaryxe2x80x9d do not attempt to distinguish importance; the terms are merely used to describe one set of flutes from the other set.
The terms xe2x80x9cprimary sealsxe2x80x9d and xe2x80x9csecondary sealsxe2x80x9d are used in the specification. These terms do not distinguish the importance of one seal over the other. Rather, primary seals refer to the seals present to plug the primary flutes and secondary seals refer to the seals present to plug the secondary flutes.
Problems and Limitations Associated with using Current State of the Art Sealing Methods
Although, the previous patents cited claim various benefits, all are constructed using the same basic technology. Little attention has been given to reducing manufacturing costs or developing new, more efficient, methods of production.
For example, the same method of sealing the filter media has been used, beginning with U.S. Pat. No. 2,599,604 issued to Bauer et. al. in June of 1952 and has continued to be described in one of the most recent patents, U.S. Pat. No. 6,235,195 issued to Tokar in May of 2001. As is described in the prior art, the basic sealing method requires that a bead of sealant be applied to the filter media, to seal the secondary flutes, as the filter element is being constructed.
One significant limitation is that the secondary seals, which are located within the secondary flutes at the end of filter element 10 opposite the primary seals located within the primary flutes, can be formed only during construction or assembly of filter element 10. When round, cylindrical elements are made the secondary seals are formed as the cylindrical element is rolled spirally forming layer upon layer. Similarly, for panel designed filters, the secondary seals are formed sheet by sheet.
The current method of constructing and sealing elements is labor intensive and does not lend itself well to efficient automated production methods. This can cause significant problems associated with product appearance, performance, manufacture and cost.
Most prior art processes also limit the types and properties of the sealing resins which can be used to construct the filter. For example, a low viscosity resin cannot be used as a sealant since it would flow and prevent sealing of the flutes. Conversely, a resin having too high a viscosity, would not wick into and anchor itself to the filter media sufficiently enough to produce a good seal. Either of these conditions would compromise filter efficiency.
It is well established in the prior art that the existing sealing beads are made wide to promote sealing and are recessed in from the edge of the filter to prevent plugging of adjacent flutes. Both of these factors serve to reduce the amount of usable filter media, thus, shortening filter life and increasing operating restriction. These limitations also produce a filter having a non-smooth, non-rigid, inlet and/or outlet face, which is less than ascetically pleasing.
The sealing methods currently being used in constructing orthogonal flow filter elements, limit the types of filter media which can be used in making the filter. The type of media used can, in turn, limit the applications to which the filter can be utilized. As an example, current sealing methods do not allow for the sealing of orthogonal flow filters made from stainless steel filter media, while using hot molten metal as a sealant; nor the sealing of polypropylene media type filters, using a hot liquid thermoplastic polymer as a sealant.
Current sealing methods do not allow for the flutes to be potted; nor can they be vertically oriented during the sealing process. Due to the viscosity requirements of the sealing resins, the layers of single-faced media must be positioned horizontally during application of the sealing bead to prevent undesirable flow of the resin which would result in inadequate sealing of the flutes.
The desired resin viscosity for the sealing bead requires that it be made wide and set far enough into the flute to prevent the resin from escaping and plugging those flutes which must remain open. Also, the further the sealant is positioned into the flute to present escape and plugging, the less media there is available for filtering, resulting in an inefficient higher initial pressure drop and shorter filter life.
Assembly problems can occur if the layers or sheets are mis-aligned when they are stacked or rolled, i.e. brought together with the sealing bead; they cannot be repositioned without damaging the seal. A filter element assembled crooked or mis-aligned, must remain so if integrity i.e. complete plugging of the flute, is to be maintained.
Finally, limits are placed upon the integrity of the media used to construct filter elements. Sealing of the primary flutes can easily be accomplished on a corrugator using relatively non-rigid, non-stiff types of filter media, since the flutes are supported by the corrugating rolls during addition of the sealing resin. However, when sealing the secondary flutes, particularly when this occurs off the machine, stiffness of the media is more critical. A certain amount of pressure must be applied to the media during the rolling, or layering of the single-faced media to ensure the sealant flows within the flutes and makes good contact with the flute walls for an acceptable plug. This pressure is necessary to ensure adequate sealing of the flutes; however, the pressure could crush the flutes of a non-rigid type media.
As an alternative to applying resin for sealing the primary and secondary flutes, it is possible to roll the two sheets of media into the composite roll and inject sealing material into each appropriate flute end, however, this would be time consuming, labor intensive and not practical from a manufacturing point of view.
The present invention describes a new method for assembling or manufacturing honeycomb filters which incorporates the vertical positioning of open flutes so they can become potted with sealing resin. My invention is applicable to either rolled filter media which forms a cylindrical honeycomb filter, or to filter media which is layered upon one another to form a rectangular shaped filter.
My process basically provides for filter media comprising both a flat-sheet and a corrugated sheet of filter material positioned one on top of the other and bonded on or near opposing sides using a sealing composition such that the sealing composition forms plugs on each side which also define confined flutes between the corrugated and flat-sheet filter material. The filter media is then assembled; either by rolling a predetermined length of the filter media; or by taking a plurality of predetermined lengths of the filter media and stacking them on top of each other. In either case, a series of substantially tubular shaped primary flutes which are plugged on both sides and a series of substantially tubular shaped secondary flutes which are unplugged are formed. One end of the filter having plugs is vertically positioned facing downward and is then inserted into a receptacle containing an amount of sealant which is sufficient for filling the unplugged flutes to a point higher than the lower plug for each of the confined flutes. After curing, the filter media is cut between the lower orientated plugs of the confined flutes but below the top surface of the sealant which filled a portion of each of the unplugged flutes. After cutting, the lower end is discarded leaving the remaining filter element which has a series of flutes which are plugged on only one end and a series of flutes which are only plugged on the opposite end.
A more detailed description for the first two embodiments is directed toward a cylindrical fluid filter for removing particulate matter, and includes a fluid impervious outer wrap, a roll of substantially flat filter media, a role of corrugated filter media, the nesting of said rolls together to form a composite filter media roll so that alternate corrugated and flat media layers are in contact, thereby forming a plurality of longitudinal flutes extending through the roll from one end to the other, the flutes being formed in two spiral series; where one series located on one side of the corrugated media are primary flutes and where the other series located on the other side of the corrugated media are secondary flutes, a sealant means disposed to plug the series of primary flutes on both ends of the composite roll so that both ends of the same flutes are sealed and fluid cannot enter through either end of the sealed flute.
For the first embodiment, the new method applies a bead of sealant to either side of the filter sheet in the manner best illustrated by the prior art in FIG. 4 of U.S. Pat. No. 3,025,963 issued to Bauer. Bauer seals both sides so that it can thereafter cut the media in half. The end result is to have two rolls of media having only one beaded side. My invention does not cut the filter media between the sealant beads to double the capacity of usable media. Rather, seals on both sides are required as will now be explained.
Once the flat-sheet and corrugated sheet have been beaded along both sides, the media is assembled by rolling the media to form a honeycomb filter which has both ends of the primary flutes sealed. If a problem occurs in the rolling process as where the created roll is uneven, the unevenness can be corrected and the media re-rolled since the secondary seals have yet to be formed.
Sealing of the primary flutes, on both ends, may be accomplished by three different means. The first example of sealing means is by laying a resin bead, at both edges of the flat sheet, between the flat and corrugated sheet as they come together while being processed through a corrugating machine. The second example of sealing the primary flutes at both ends is by forming a continuous resinous film over the ends of the flutes after the media is corrugated. The third example of sealing means is by collapsing both ends of the primary flutes, while, in some cases, adding a small amount of resin to the flute ends to ensure closure, or in some applications, thermally welding the primary flutes closed. Any single method or combination of these three methods may be used to seal the primary flutes on either or both ends of the roll, depending on the type of filtering application and the type of filter media required.
When the filter media is wound upon itself, it forms a second series of flutes, termed secondary flutes which are open on both ends. No seals are applied to the structure as it is being wound, as is the case in the prior art.
After winding, the resulting filter structure is vertically positioned and then inserted for potting by positioning it within a receptacle which can be made from, as examples, fiberboard, or PVA plastic containing, a predetermined level of self-curing resin. The outside diameter of the filter structure is almost the same dimension as the inner diameter of the tubular housing so that the annular space therebetween is negligible or non-existent.
As an example for the amount of resin to be used, a 0.25 inch deep pond of a one or two-part self-curing resin is placed within a tubular housing, sealed at the bottom to prevent leakage of the resin. As the roll of a predetermined length of filter media is potted or pushed down to contact the bottom of the tube, the resin is forced to flow up, and into, the secondary flutes and any other open areas of the structure face. The resin cannot flow into the primary flutes due to the primary seals which were formed as discussed earlier. The amount of resin positioned within the tubular housing is predetermined by which method is used to seal the primary flutes, being sufficient so that the resin level within the secondary flutes rises to a sufficient height above the primary flute seals.
At this stage, the manufacture can continue using either a preformed tube or a to-be-formed shell around the periphery of the filter.
Preformed Tube Embodiment
For this embodiment, a receptacle which comprises a preformed tubular housing is provided, which has a sufficient length and diameter to accept the media within, is stood on one end with its bottom end having a temporary impervious seal to prevent leakage of the potting resin out the bottom of the tube. The impervious seal can consist of, for example, a thin sheet of metal foil, plastic, or paper, bonded across the base end of the tube.
Once the filter media is displaced completely into the tube so that its lower end contacts the seal at the base end of the tube, and the resin has reached a maximum surface level height in the secondary flutes, the resin is allowed to cure.
Following curing and hardening of the resin, both the primary and secondary flutes are found to be sealed at the base end. Next, part of the lower end of the tube, filter media structure and tube sealant, is cut off at an appropriate height, thereby causing the primary flutes to become open while the secondary flutes remain sealed. This process produces a finished filter whose open flutes on either the upstream or downstream end of the filter are sealed on the opposing end. Thus, any fluid entering the open flutes on either end of the roll must pass through the filter media, thus being filtered, before exiting via the other series of open flutes on the other end.
Resin Molded Shell
A second embodiment is a slight variation where, instead of the receptacle being a tubular housing as discussed in the preformed tubing embodiment earlier, the receptacle is a tubular mold. The media is inserted in the same manner as above but is centered so that a substantially uniform annulus is maintained. Once the media is completely inserted into the mold and the sealant level has risen into the secondary flutes as described above, a shell forming means, preferably additional sealant or resin is next injected or delivered into the annular region of the mold from above. Time is provided for curing and then the resin formed shell and filter are ejected or removed from the mold and then cut in the same manner as described for the first embodiment. However, the advantage of this variation is that since the shell is formed directly on the outer circumference of the filter media, the shell serves to protect and help seal the filter better than can be expected for the first embodiment.
The above process produces a finished filter, containing a rigid outer impervious shell, whose open flutes, on the inlet or outlet end of the filter, are sealed on the opposing end.
Rectangular Filter Variation
A final variation of the process is directed to the manufacture of a rectangular fluid filter housing comprising a top, bottom, two sides, a front, and a back. The top, bottom and two sides of the filter housing being fluid impervious.
The assembly step for this embodiment comprises the stacking of a plurality of filter media one on top of the other. In this embodiment, the predetermined lengths are smaller than for the tubular filter elements of the first two embodiments since smaller lengths are required for stacking. The stacking of the filter media is done so that the corrugated sheets of adjacent stacked filter media do not contact each other. The stacking is aligned so that confined flutes with plugs on either side are formed and open flutes on either side are formed.
As in the first two embodiments discussed earlier, a receptacle is required for holding a predetermined amount of sealant which will fill the open flutes when the stacked filter media is vertically orientated and inserted into the sealant and allowed to cure.
Sealant means are made as is discussed in embodiments one and two above, using one or a combination of the three sealing methods described to seal the primary flutes. Secondary flutes are sealed through the potting process described earlier, after which, the filter element is cut-off near its base end in a manner as discussed earlier for the cylindrical filter. This process produces a finished filter, with a preexisting housing, or, with a resinous outer shell, whose open flutes on either the upstream or downstream end of the filter are sealed on the opposing end. Thus, any fluid entering the open flutes on either end of the filter must pass through the filter media in order to exit via the other series of open flutes on the other end and is thereby filtered.
The specific sealing methods used to seal the flutes could also potentially be used to seal opposing flutes on sintered ceramic honeycomb substrates, such as those being used as substrates in catalytic converters, heat exchangers and/or diesel particulate filters, however, in these cases ceramic sealants would be preferred.